We have stainless steel thermoses that we fill with heated water to pre-heat the scopes. Scopes need at least 5 to 10 minutes to soak for this to work. After taking the sope out of the water, dry it, then apply small amount of anti-fog, and rub that dry before putting into the patient.
The reason why the scopes are fogging is that they are appx. 64-68 degrees F, and being placed in a body that's 98 F or so. Also, if the CO2 is not heated as it's going into the patient, that can fog a scope as well. Making sure that the scope port isn't also the insufflation port can help this.